Electron discharge device and method of making the same



May 17, 1966 A c. E DONER 3,252,043

ELECTRON DISCHARGE DEVICE AND METHOD OF MAKING THE SAME Filed May 14, 1962 IIIIIIIIIIIIIIIIIIIIIIIIII II/IIIIIIHIIHHIIIIIIIIIII INVENTOR. 6244/05 5'. 004/54 OAQM IITORA/Ey United States Patent 3,252,043 ELECTRON DISCHARGE DEVICE AND METHOD OF MAKING THE SAME Claude E. Doner, Lancaster, Pa., assignor to Radio Corporation of America, a corporation of Delaware Filed May 14, 1962, Ser. No. 194,506 4 Claims. (Cl. 313-348) The present invention relates to electron discharge devices and particularly to a beam power pentode.

An object of the invention is to provide an electron dis charge device characterized by improved operation at ultra high frequencies of the order of 500 megacycles.

Another object is to provide an improved method of assembling an electron discharge device.

A feature of the invention contributing to improved operation of the device is the provision of a relatively low impedance element, bypassing the screen grid of the device to the cathode thereof, to permit grid driven operation of the device. The low impedance element is disposed internally of the device to avoid objectionable lead inductance to an external bypass capacitor.

Another feature of the invention involves a novel suppressor grid structure. This structure contributes appreciably to the efliciency of the device. To this end the suppressor grid of the invention serves to correct an adverse condition encountered in prior tetrode types of electron discharge devices. This adverse condition arises as a consequence of an axial divergence of the electron beam to end portions of the device. Such divergence allows the beam to reach the anode at portions thereof where the screen grid is ineffective to produce a space charge repelling the secondaries from the anode. The suppressor grid according to the invention has a novel structure for effectively restraining an axial divergence of the electron beam, thereby confining secondary origin to a region controlled by space charge.

A further feature of the invention concerns a novel cathode support having the advantages of ruggedness and of facilitating manufacture of the device.

Further objects and advantages of the invention will become evident from the following and more detailed consideration of an example of anelectron discharge device embodying the invention.

In the drawing, the sole figure shows an elevation in cross-section, of an electron discharge device embodying the features and advantages aforementioned.

The device shown comprises an anode defining a space within which are housed a complement of electrodes including a tubular cathode having an electron emitting coating 14 on its outer surface. The cathode 12 is supported at one end by a tubular support 16 over which it is telescoped. The support 16 is fixed to an insulating member 18, made of ceramic for example, and having three electrically insulated metallized coatings 20, to one of which support 16 is brazed or otherwise joined. The other end of the cathode 12 is fixed to ametal sleeve 22 as by brazing or welding. The cathode 12 is integral with a support 24 thinned down to reduce heat losses from the cathode. The support 24 terminates at one end in a flange 25 sealed in a suitable manner across an opening in the device envelope, as by a radio frequency braze.

The cathode 12 is heated to electron emitting temperature by means of a heater structure comprising a coil of wire 26, made of tungsten, for example, and having an insulating coating 28 thereon, such as aluminum oxide. The upper end portion of the coil 26 is free of insulating coating material and is fixed as by brazing to the upper end, as viewed in the drawing, of a metal rod 30, made of molybdenum for example. The lower end portion (not shown) of the coil is also uncoated and is fixed to the sleeve 22. The rod 30 insulatingly extends through the device envelope to form an external contact terminal 32. The rod 30 is insulated from the device envelope by means of an insulating ring 34, made of ceramic for example, and which is sandwiched between a metal ring 36 fixed to flange and to one face of thering 34, and a metal 42, 44, and an annular portion on the upper end surface of the member. The control grid 40 is fixed to a portion of the insulating member 18, spaced by slot 42 from the coated portion of the member to which the cathode support 16 is fixed. In this way, the upper end portion of the grid 40 is electrically insulated from the cathode 12. The lower end of the control grid 40 terminates in an outwardly flaring flange 46. The flange 46 is fixed to three lead-in prongs, angularly spaced 90, two of the latter prongs, 48, 50, being shown. Each prong has a flat head portion 52, the top surface of which engages the grid flange 46. The prongs referred to are insulated from metal envelope portion 54 by enlarged aperture 55 through the latter which are spanned by insulating rings 56, which may be made of ceramic. The rings 56 are initially metallized for brazing to the underside of the heads 52 and to the inner surface of envelope portion 54. The grid flange 46 is slitted at 58 so as to be out of engagement with the upper end surface of a contact prong or terminal 60 to be described.

Concentrically surrounding the control grid 40 is a screen grid 61 having an upper inturned portion fixed to insulating member 18at a portion thereof separated by slot 44 from the portion of the member to which the control grid 40 is fixed. In this way the upper end of the control grid is electrically insulated from the upper end of the screen grid. The lower end portion of the screen grid 61 includes an area 62 that is frusto-conical, i.e., that constitutes a frustum of a cone, and an outwardly extending flange 64. The flange 64 is brazed to the upper surface of the contact prong 60. The prong 60 is insulated from the metal envelope portion 54 by means of an insulating ring 65 suitably metallized to provide brazing surfaces. The flange 64 is insulated from the other three contact prongs byrneans of an insulating tube 66 interposed between each of such other three contact prongs and flange 64. A metal ring 68, made of Kovar for example is preferably interposed between the flange 64 and each of the insulating tubes 66, to provide a closer match to the expansion characteristics of the tubes 66, than the metal of the flange 64. For facilitating jigging, the four contact prongs'referred to are provided with axially extending recesses 69, aligned with openings in the elements associated with the prongs, such as the tubes 66, screen grid flange 64 and control grid flange 46.

The suppressor grid comprises a two-part structure. One part includes an upper metal cap portion 70, as viewed in the drawing. The cap portion 70 is suitably fixed as by brazing to a metal cup '71 which has previously been brazed to the conducting coating on the insulating member 18; The cylindrical portion of the cap 70 preferably extends downwardly approximately to the plane of the upper terminus of the emitting cathode coating 14, and concentrically surrounds the upper portion of the screen grid 61. For providing. electrical connection between the cap 70 and the cathode 12, the wall of the channel 72 extending axially through the member 18, is provided with an electrically conducting 7 material such as titanium dioxide or mica.

coating as aforementioned, connecting the coating portions to which the cup 71 and cathode supportv 16 are fixed. The other part of the suppressor grid structure includes a cylindrical portion 74 extending upwardly substantially to the lower terminus of the cathode coating 14. V The cylindrical portion 74 is concentric with and surrounds the lower part of the screen grid 61. The part of the suppressor grid under consideration also includes an outwardly flared vfrusto-conical portion 75 for strength, and anoutwardly extending flange portion 76.. The underside of the flange portion 76, as viewed in the drawing, contacts, without brazing, the upper face of an insulating ring 78 having an important function to be described. The lower face of the ring 78 is also in brazeless contact with the upper face of the screen grid flange 64.

The ring 78 constitutes a dielectric, electrically insulating and closely separating the screen grid 61 from the flange 76 .electricallyconnected to the cathode 12 and the suppressor grid portions 70 and '74. Actually, with respect to alternating current, the ring 78 serves as a by-pass capacitor. Its disposition within' the device envelope avoids the need for leads to an external capacitor, and the capacitor system shown is therefore free from objectionable inductance effects associated with such leads. The ring 78-may be made of an insulating Where mica is used it is preferred that the faces of ring 78 be metallized with a coating made of gold.

The metal envelope portion 54 previously referred to, includes a cylindrical flange 80. A metal ring 82 has a cylindrical flange 84 welded to flange 80 and the ring 82 exerts a continuing pressure on a flexible metal ring .86, for ruggedizing the device structure. The ring 86 may be made of a springy metal such as stainless steel, and in its normal unstressed condition the ring constitutes a structure that is slightly frusto-conical. When flattened out as shown in the drawing the ring 86 exerts a continuing force tending to separate ring 82 and flange 76 against the restraint of weld 88 and to urge the flanges 64, 76 into good surface engagement with the capacitor insulator 78. The magnitude of the fiexure of the ring 86 from its fr-ust-o-conical shape to its flattened form is within the elastic limits of the material of the ring. This manner of mounting of the lower suppressor grid portion 74 causes it to be electrically connected to cathode 12.

The ring 82 is brazed to one metallized end of an insulating ring 90, which may be made of ceramic for example. The other metallized end of ring 90 is brazed to a metallic flange 92 that is brazed or otherwise fixed to an end portion 94 of reduced thickness of the anode 10. The flange 92 made of Kovar for example, is shaped to produce strain isolation between ring 90 and anode 10. Primary heat dissipation from the anode is eflfected by means of a finned radiator 96 having louvers 88 for intercepting cooling air from a forced air stream, or from air given movement by convection. The outer ends of the fins constituting the radiator 96, are engaged 'by a cylindrical metal sleeve 100 and brazed thereto by a brazing material102. The cylindrical sleeve 100 may serve as the lead-in terminal for the anode It); The envelope of the device is exhausted through metal tubulation 104, the tubulation thereafter being closed by a cold weld pinch-elf 106.

The metallized coatings generally referred to in the foregoing, on the several insulating \members, may comprise a primary coating of molybdenum having thereon a plated coating of nickel. The brazing material used may be BT solder in certain areas, and Nioro solder in other areas. These solders are available commercially under the trade names indicated. This selection preserves previously made seals byvirtue ofthe different melting point temperatures of these solders.

The structure of the device described in the foregoing conveniently lends itself to an advantageous method of assembly. In practicing the method it is preferable first to form several subassemblies. The composition of each sub-assembly is so chosen that the jigging of the parts is facilitated.

One subassembly may consist of the cathode support 16, the insulating member 18, the control grid 49 and the metal cup 71. Each of these elements has an opening shown at the upper portion of the drawing, the several openings being of the same size proper orientation thereof by a mandrel of a jig (not shown). Thus, the openings 106 and 108 in the cup 71 and cathode support 16 respectively, are of the same size as the opening or channel 72 in insulating member 18. A rectilinear man: drel extending throughthese openings will fully position the cup 71 and the insulating member 18, and partly position the control grid 40 and the cathode support 16. A complete positioning of the control grid 40 and the cathode support 16 in the assembly may be effected by suitably stepped cylindrical portions of the mandrel adapted. to engage snugly the inner surfaces of the control grid 40 and the cathode'support 16. Suitablestops on the mandrel may-be provided for engaging the lower ends of these parts. The parts thus assembled on the jig may be placed in an oven having a non-oxidizing atmosphere such as hydrogen, for brazing the parts to the metallized coating 20 on the insulating member 18. The oven temperature may be about 950 C., and the brazing material is preferably Nioro solder.

The resultant subasse mbly in which the parts thereof are fixed, may then be included in a second subassembly. In building up the second subassernbly the envelope portion 54 is placed in a suitable jig having areference surface adapted to engage the outer surface of flange portion 80 for centering the envelope portion 54. Rings 56 and 65, made of insulating material, are then placed over opening in the envelope member 54 and in substantial coaxial relation with such openings. The envelope portion 54 is then rotated axially until the openings in the insulating'members 56;, 65, and in theenvelope portion 54, are aligned with elongated cavities in the jig adapted to receive the lower portions of the four terminals or contact prongs 48, '50, (the fourth prong not being shoWn).- The four prongs referred to are then inserted through the aforementioned openings in the rings 56, 60, and in the envelope portion'54 and into the cavities in the jig. Thereafter a mandrel is in- 50 'serted into each cavity 69 of the three control grid terminals or prongs. Flange 46 of the control grid 40 of the previously'formed subasseinbly is then extended over the mandrels, the latter passing through openings provided in the flange for accurately positioning the 'control grid. Thereafter, insulating tubes 66 and Kovar washers 68 are threaded over the mandrels to rest on the control grid flange 46. The screen grid 61 is then threaded over the parts thus assembled, until walls defining its upper opening snugly engage the periphery of insulating member 18-, and holes in its flange 64 receive the three'rnandrels aforementioned, and the flange 64 rests on Kovar washers 68 and the upper end surface of screen grid contact terminal 60, with BT solder interposed therebetween.

The assembly thus loosely mounted is then placed in an oven containing a non-oxidizing atmosphere such as hydrogen, and at a temperature of about 800 (3., for brazing'the parts together.

After the control grid 40 and the screen grid 61 have been thus fixed in relation to each other, they are subjected to an operation involving the cutting of radially registering slots in the side walls thereof. The operation may beperformed by an erosion technique involving electrical discharge machining. This technique is described fully in United States Patent No. 2,980,984, issued to M. B. Shrader 'et al. 'on April 25 1'961.

Thereafter the insulating ring 78 is threaded over the sub-assembly until it rests on flange 64. It is axially self is selfjigged by a relatively snug engagement betweenwalls defining a central opening therein, and the outer peripheral surface of cup 71. Cap 70 is fixed to cup 71 by means of a radio frequency braze.

To the three-grid sub-assembly thus formed is then added the spring 86, which is placed over the suppressor grid flange 76- and jigged into approximate position by the frusto-conical portion 75 of the suppressor grid part 74.

A separately formed sub-assembly consisting of the anode with exhaust tubulation 1G4, flange 92 and insulating tube or ring 90 and flange 82, is then jigged to dispose its parts in coaxial relation. While so jigged the parts are again subjected to oven heating at about 800 C. in a non-oxidizing atmosphere such as hydrogen, for brazing the loosely assembled parts together.

The separately formed sub-assembly referred to, is then joined to the aforementioned three-grid sub-assembly to which the spring 86 has been added. In joining the two sub-assemblies, the metal ring 82 with its cylindrical flange 84, is telescoped into the cylindrical flange 80, and appreciable axial pressure is applied to the ring 82 against a stop (not shown) engaging the lower end of the device envelope, to substantially flatten the ring or disc 86 and thereby constitute it a source of continuing pressure of the flanges 64, 76 against opposite faces of the dielectric member 78, after the flanges 80, 84 have been mutually fixed. Instead of the ring or disc form shown, the member 86 may comprise a'body of relatively thin tungsten wires resiliently crushed between the flanges 82 and 76. While the axial pressure is being applied, as indicated, the two flanges 80, 84 are fixed to each other by means involving localized heat, such as heliarc welding. Such localized heat preserves previously made brazes from harm.

The final sub-assembly formed during manufacture of the device, consists of heater 26, 28, support rod 30, support sleeve 22, the cathode 12 with its thinned down portion 24 and flange 25, insulating ring 34 and metal rings 36, 38. This final sub-assembly after mutually fixing the parts thereof, is self-jigged into the previously made subassembly, by telescoping the cathode end of the final assembly over the cathode support 16, until the latter bottoms on a ledge or shoulder 110 formed within the cathode. Such telescoping step axially orients the upper end of the final sub-assembly with the previously completed sub-assembly. The lower end of the final assembly is disposed in coaxial relation with the previously formed sub-assembly by means of a relatively snug fit between the outer surface of the cathode flange 25 and the inner surface of the envelope flange 112. When suitably oriented, the final assembly is fixed in desired position by means of a radio frequency braze 114 between the flanges 25 and 112. This type of braze is preferred since it is made by a localized heat that involves a minimum of harm to the assembled cathode.

The device is particularly advantageous in grid drive operation. In this type of operation the flange 80 may serve as a low inductance input terminal to the cathode, while the sleeve 100 may serve a similar function with respect to the anode. In addition, to reduce lead inductance to the control grid, the latter is served by three relatively massive terminal members or prongs 48, 50 (the third not being shown). The screen grid is served adequately by a single relatively thin terminal member 60. This difference in terminal member thickness is also of advantage in orienting the device in a socket.

What is claimed is:

1. An electron discharge device comprising:

(a) a tubular cathode having an electron emitting coating on an annular portion thereof,

(b) a tubular control grid surrounding said cathode and having an apertured region axially coextensive with said annular portion,

(c) a screen grid surrounding said cathode and having an apertured region axially coextensive with said coated annular portion, the apertures in said grids being aligned radially,

(d) a suppressor grid having a first imperforate tubular part extending from a region remote from said coated annular portion of the cathode and to substantially the plane of one end of said annular portion,

(e) said suppressor grid having a second imperforate part spaced from said first part and extending from a region remote from said annular portion and substantially to the plane of the other end of said annular portion,

(f) a tubular anode surrounding said two suppressor grid parts and the region between said two parts, and

(g) means electrically connecting said two suppressor grid parts.

2. An electron discharge device comprising:

(a) a complement of tubular concentric electrodes including a cathode having an electron emitting region,

(b) a first tubular imperforate suppressor grid part surrounding one end portion of said complement of electrodes and extending to one terminal plane of said emitting region,

(c) means including a metallic coating connecting said suppressor grid part to said cathode,

(d) a second tubular imperforate suppressor grid part surrounding the other end portion of said complement of electrodes and extending to the other terminal plane of said emitting region, said second tubular suppressor grid part having an outwardly extending radial flange, and

(e) an electrically conducting support for said cathode,

said flange being electrically connected to said support.

3. An electron discharge device having a cathode adapted to emit electrons to form a beam, and a suppressor grid adapted to converge the beam axially of the device, said suppressor grid comprising:

(a) an imperforate metallic cap having a tubular portion extending around one end portion of the beam path and an apertured closure portion, and r (b) an imperforate tubular member extending around the other end of said beam path, said tubular member having an outwardly extending flange,

(c) said closure portion and said flange being electrically connected to said cathode.

4. An electron discharge device comprising:

(a) a tubular screen grid having an outwardly extending radial flange,

(b) a cathode having an annular electron emitting coating thereon,

(c) a first tubular suppressor grid part surrounding a i portion only of said screen grid and extending to one terminal region of said coating,

(d) a second tubular suppressor grid part surrounding another portion only of said grid and extending to the other terminal region of said coating,

(e) one of said suppressor grid parts having an outwardly extending radial flange, said flanges being spaced axially of the device and including coextensive regions, said suppressor grid parts being connected to said cathode,

(f) a flat member made of dielectric material positioned between said coextensive regions, and

(g) means including a spring member under compression for urging opposite surfaces of said flanges at 7 8 said regions into forced surface contact with opposite 2,849,640 8/ 1958 Stephens 313-292 faces of said dielectric member. 2,945,150 7/1960 De Santis et a1. 3'13-346 2,986,671 5/ 1961 Krstetter et a1. 313-346 Rferences Cited by the Examiner V UNITED STATES PATENTS 5 JOHN W. HUCKERT, Primary Examiner. 2,261,154 11/ 1941 Hansen et a1 313-248 H Q Examiner- 2,464,241 3/1949 Krim -2 L. ZALMAN, Assistant Examiner, 2,515,267 7/1950 Salisbury 313-348 

1. AN ELECTRON DISCHARGE DEVICE COMPRISING: (A) A TUBULAR CATHODE HAVING AN ELECTRON EMITTING COATING ON AN ANNULAR PORTION THEREOF, (B) A TUBULAR CONTROL GRID SURROUNDING SAID CATHODE AND HAVING AN APERTURE REGION AXIALLY COEXTENSIVE WITH SAID ANNULAR PORTION, (C) A SCREEN GRID SURROUNDING SAID CATHODE AND HAVING AN APERTURED REGION AXIALLY COEXTENSIVE WITH SAID COATED ANNULAR PORTION, THE APERTURES IN SAID GRIDS BEING ALIGNED RADIALLY, (D) A SUPPRESSOR GRID HAVING A FIRST IMPERFORATE TUBULAR PART EXTENDING FROM A REGION REMOTE FROM SAID COATED ANNULAR PORTION OF THE CATHODE AND TO SUBSTANTIALLY THE PLANE OF ONE END OF SAID ANNULAR PORTION, (E) SAID SUPPRESSOR GRID HAVING A SECOND IMPERFORATE PART SPACED FROM SAID FIRST PART AND EXTENDING FROM A REGION REMOTE FROM SAID ANNULAR PORTIN AND SUBSTANTIALLY TO THE PLANE OF THE OTHER END OF THE ANNULAR PORTION, (F) A TUBULAR ANODE SURROUNDING SAID TWO SUPPRESSOR GRID PARTS AND THE REGION BETWEEN TWO PARTS, AND (G) MEANS ELECTRICALLY CONNECTING SAID TWO SUPRESSOR GRID PARTS. 